Confirmed and presumed canine insulinomas and their presumed metastases are most conspicuous in the late arterial phase in a triple arterial phase CT protocol

Adrianna Skarbek, Virginie Fouriez-Lablée, Helen Dirrig, Francisco Llabres-Diaz

Background: Insulinomas are pancreatic tumors that cause hypoglycemia and hyperinsulinemia in dogs. Contrast-enhanced computed tomography (CECT) is a common imaging modality for detecting and staging insulinomas. However, the optimal contrast phase and enhancement pattern of canine insulinomas are not well established.

Study: The authors conducted a retrospective observational study of 12 dogs with confirmed or presumed insulinomas that underwent quadruple-phase CECT. They described the contrast enhancement (CE) pattern of pancreatic nodules and presumed metastases in three consecutive arterial phases (early, middle, and late) and a venous phase. They also evaluated the visual grading score (VGS) of the CE of each lesion on a 4-point subjective scale.

Methods: The authors reviewed the medical records, biochemistry, and CECT images of the included dogs. They identified and characterized the arterial phases based on the opacification of the hepatic arteries, portal vein, and caudal vena cava. They recorded the presence, number, location, and VGS of the pancreatic nodules and presumed metastatic lesions in each phase. They also estimated the radiation dose and compared it with other oncological and dynamic CT studies.

Results: The authors found that 17 pancreatic nodules and 23 presumed metastatic lesions showed arterial hyperattenuation in CECT. The late arterial phase (LAP) provided the highest enhancement scores for the majority of lesions (76%), followed by the middle arterial phase (MAP) (88% for pancreatic nodules and 50% for presumed metastases). The early arterial phase (EAP) and the venous phase (VP) showed mostly none/inconspicuous enhancement. The LAP was achieved at a median time of 39.5 seconds after contrast injection. The estimated radiation dose was lower than other CT studies.

Limitations: The main limitations of the study were the small sample size, the retrospective design, the lack of histopathological confirmation for all lesions, the variability of scanning and injection protocols, and the use of a 320-slice CT scanner that is not widely available for veterinary use.

Conclusions: The study supported the previous findings that canine insulinomas and their metastases show arterial hyperattenuation in CECT. The authors recommended the inclusion of LAP (and/or MAP) in the standard insulinoma protocol, as they improved the detection and localization of the lesions. They also suggested using a fixed injection duration technique and a bolus tracking method to obtain consistent arterial phases.

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